Automatic shutter control circuit

ABSTRACT

The present invention relates to an automatic camera shutter control circuit and more particularly to an automatic shutter or exposure control circuit for a T.T.L. type single lense reflex camera having a constant voltage circuit. The invention thus relates to an electric shutter circuit having a control circuit for maintaining constant the voltage between terminals of a photosensitive element which measures the amount of light from a photographed object and generally comprises improvements in information storage and retrieval, and especially to a circuit for the automatic timing of camera shutters in response to light sensed by a through-the-lens light measuring system.

United States Patent [1 1 111 3,763,751 Akiyama Oct. 9, 1973 AUTOMATICSHUTTER CONTROL 3,602,717 8/1971 Konig 95/10 X CIRCUIT 3,641,890 2/1972Ono 3,678,826 7/1972 Mori et al. 95/l0 [75] Inventor: Taiichi Akiyama,Okaya,.lapan [73] Assignee: Yashica Co., Ltd., Tokyo, Japan PrimaryExamine, samue1 Matthews 22 Filed; a 22 1 72 Assistant Examiner-MichaelL. Gellner Atto --J bs & Ja b [2]] Appl. No.: 255,400 mey aco co 5Related u.s. Application Data [63] Continuation-impart of Ser. No.835,523, June 23, [57] ABSTRACT 1969' The present invention relates toan automatic camera shutter control circuit and more particularly to anau- [30] Foreign Application Prlorhy Data tomatic shutter or exposurecontrol circuit for a June 29, 1968 Japan 43/54779 T.T.L. type singlelense reflex camera having a cons- June I963 p 43/54780 tant voltagecircuit. The invention thus relates to an July 1,1968 Japan 43/55012 elet i shutter circuit having a control circuit for maintaining constantthe voltage between terminals of [52] 11.8. CI. 95/10 CT aphotosensitive element which measures the am n [51] Int. Cl. G03b 7/08of light from a photographed object and generally [58] Field of Search95/10 CT om rise improvements in information storage and retrieval, andespecially to a circuit for the automatic Referencesciled timing ofcamera shutters in response to light sensed UNITED STATES PATENTS by athrough-the-lens light measuring system. 3,470,798 10/1969 Miyakawa95/10 24 Claims, 6 Drawing Figures TIMING AND 1 SWITGHING GlllllUll 25'Ell PATENTEDU I 3.763.751

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sum 30F a HAL VARIABLE l] T MINING NE E TMNSISTUR QURRESI 206 TIMINGBAPAGHUR 205 UUNSTANT BURHE Pumucmm NT comm TRANSISTOR 202' AUTOMATICSHUTTER CONTROL CIRCUIT The present application is aContinuation-in-Part of application Ser. No. 835,523, filed June 23,1969, for Memory Control Automatic Camera Shutter, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to anautomatic camera shutter control circuit. More particularly, theinvention relates to an automatic shutter or exposure control circuitfor a T.T.L. type single lens reflex camera having a constant voltagecircuit. The invention relates to an electric shutter circuit having acontrol circuit for maintaining constant the voltage between terminalsof a photosensitive element which measures the amount of light from aphotographed object. Thus, the invention generally comprisesimprovements in information storage and retrieval, and, moreparticularly, to a circuit for the automatic timing of camera shuttersin response to light sensed by a through-the-lens light measuringsystem.

As used herein, T.T.L. means through the taking lens. A T.T.L. typeautomatic exposure control single lens reflex camera with an electricshutter is known.

ln the storage of information which has been converted into acorrespondingly varying electrical parameter, it is common to utilize amemory circuit comprising a combination ofa field effect type (F.E.T.)transistor of high input impedance and a memory capacitor. In a memorycircuit of this type, however, the gatesource voltage of the fieldeffect transistor is generally non-linearly related to the drain currentdue to the characteristics thereof, so that a gate input of a value tobe stored undesirably tends to be in non-linear relationship with thecorresponding drain output. Furthermore, when the drain current isutilized as a parameter to be stored, the drain current characteristicrelative to the drain-source voltage tends to curve sharply in socalledtriode range and pentode range (the curving point normally correspondsto an operative voltage of about 2 volts), so that such a field effecttransistor cannot be used at a relatively low voltage. Field effecttransistors, in addition, are non-uniform, depending on the individualproducts, in gate voltage relative to drain current pinch-off due to aconstruction peculiar to a transistor of this'type, even if they are ofthe same model, and the non-uniformity with respect to this property ismore pronounced than with respect to the other characteristic such asthe vacuum tube characteristic. On the other hand, a leak in thecapacitor or of the insulation of the distributing board combined withthe field effect transistor is so high, although the input impedancethereof is high, that the field effect transistor generally fails toaccomplish the desired function as a memory of this type.

SUMMARY OF THE INVENTION The principal object of the present inventionis to provide a highly reliable, improved storage or memory deviceutilizing a field effect transistor. It has usually been necessary thata battery supplying a higher operative voltage be utilized as a powersource in an electric shutter mechanism having such a memory. It hasalso usually been necessary to provide a high order of amplification ofthe electrical information of illumination intensity of an object to bephotographed, so that an electric shutter mechanism having a memory ofthe subject type may be useful for a wide range of light values. Thelarge-sized battery and the high multiplicity of circuit elements,however, have resulted in a bulky mechanism which cannot be easilyincorporated into a small-sized camera and is highly expensive.

Another object of the invention is to provide an automatic electricshutter control circuit of simple construction and capable of utilizinga small battery. In such shutter control circuit, any leakage currentoccurring in the timing capacitor or in the storage or memory capacitorwould greatly adversely affect the correct control of exposure time, sothat the leakage current involved in these capacitors would aggravatethis effect and, particularly in the control of exposure, even a slightleakage current might considerably vary the exposure time to becontrolled. Furthermore, it is very difficult in practice to completelyavoid any leakage occurring in capacitors of this type since, even whenan element of high input impedance such as a field effect transistor isutilized as a circuit element with the capacitors, the insulationresistance of members, such as a print base board on which each of thecapacitors is mounted, a switch, or an insulator, is frequently lowerthan desired due to factors including atmospheric humidity.Consequently, in an electric shutter control circuit having a memory ofconventional type, the control of exposure for a long time has beengreatly limited.

Still another object of the invention is to provide an improved electricshutter control circuit in which any leakage current in the timing andmemory capacitors may compensate one another, so that the exposures areand can be accurately controlled for long periods of time.

The invention provides a novel exposure control circuit which is able tooperate on a short time storage or memorization of exposure controlinformation. That is, the shutter control circuit of the nvention is apractical circuit of high stability which automatically makes anexponential function of the brightness of the object accuratelycorrespond to the shutter speed utilizing the. principle of a constantvoltage circuit.

In one sense the present invention contemplates a shutter controlcircuit comprising a negative feedback network including a firsttransistor and a variable resistance information member for producing afirst signal responsive to the relationship of the resistances of thefirst transistor and the variable resistance information member. Asecond means produces a second signal. A third means produces a thirdsignal reponsive to the difference between the first and second signals.An amplifier having a high input impedance and an output is provided. Astorage or memory capacitor is connected to the input of the amplifier.The third signal is applied to the input of the amplifier. The output ofthe amplifier is coupled to the input of the transistor in a phase toform the negative feedback network.

In the automatic shutter timing circuit of the invention, aphotoconductor and a timing capacitor are alternatively connected via aswitch in series with a first transistor across a battery. The voltagedifference between the voltage at the collector electrode of thetransistor and an adjustable voltage derived from a voltage divider isapplied to the base electrode of a second transistor whose output isderived from its collector electrode and is amplified and alternatelyapplied to a shutter closure release controlling solid state switch andthe gate of a field effect transistor. The source of the field effecttransistor is connected to a point at ground potential through theresistance element of a potentiometer connected in series with aconstant voltage diode. The potentiometer has a movable contact orelectrode connected to the base electrode of the first transistor ininverse or negative feedback. A storage or memory capacitor is connectedbetween the gate of the field effect transistor and the end terminal ofthe potentiometer remote from the source of th field effect transistor.

The control circuit of the invention is of simple structure, reliableand accurate in operation, and is not'adversely affected by ambientconditions and nonlinearity and non-uniformity of the solid statecomponents.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a block diagram illustrating the principle of operation of theautomatic shutter control circuit of the invention;

FIG. 2 is a circuit diagram of a first embodiment of the automaticshutter control circuit of the invention;

FIG. 3 is a circuit diagram of a second embodiment of the automaticshutter control circuit of the invention;

FIG. 4 is a block and circuit diagram of a third embodiment of theautomatic shutter control circuit of the invention;

FIG. 5 is a circuit diagram of a fourth embodiment of the automaticshutter control circuit of the invention; and

FIG. 6 is a circuit diagram of a fifth embodiment of the automaticshutter control circuit of the invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, a control component ortransistor 1 controls a load voltage V and controls a signal obtained byamplifying a difference detected by comparing the load voltage V0 with areference or standard voltage Vc applied to said control transistor. Theload voltage V0 is controlled via a feedback circuit, or the like. Thevoltage control involves a power source voltage Vin applied to inputterminals 2 and 3. The voltage V0 is applied to a load 4 via the controltransistor 1.

When the load 4 varies and the load voltage Vo varies, the variation orvarying position of the load voltage is detected by a feedback circuit5. A standard voltage source 6 provides the standard voltage Vc. Thesignal produced by the feedback circuit is compared with the standardvoltage Vc. A signal representing the difference between the feedbacksignal and the standard voltage is amplified by an amplifier 7. Theamplified signal is supplied to the transistor 1 and varies the outputcurrent of said transistor in a manner which maintains the voltage V0 ofthe load 4 constant. Thus, for any load fluctuation, the controltransistor 1 controls the current flowing through the load by its outputcurrent, so that the load voltage V0 is maintained constant.

The invention utilizes the aforedescribed principle and utilizes aT.T.L. single lens reflex camera electric shutter in the embodiments ofFIGS. 2, 3, 4 and 5.

In the embodiment of FIG.'2, a stable electric battery or cell 8 isconnected to input terminals 9 and 11 of a constant voltage circuit as apower source. A photocell or photoconductive element 12 is connected asa load to an output terminal 1'3 ofa control transistor 14. A switch 15connected to *the terminal, l3 of the load functions to close a contact15a before the shutter is actuated for applying the voltage Vo acrossthe load 12 to the gate of a first field effect transistor or F.E.T. 16.The first F.E.T. l6 detects the load voltage V0.

The load voltage Vo determinesthe' operating point by serving as a gatevoltage. A second F.E.T. 17 having the same characteristics andperformance as the first F.E.T. 16 is connected to said first F.E.T. asa differential amplifier. This differential amplifier 16, 17 has theimportant advantage that the amplification is very stable. This is dueto the temperature characteristic of each F.E.T. being offset againstthe other because of its balanced operation simultaneously with thereversal of the amplified phase of both F.E.T.s. Furthermore, asreferred to hereinafter, the differential amplifier of F.E.T.s 16 and 17is advantageous because the equal phase noise which influences theshutter operation may be extinguished.

The balance type amplifier of F.E.T.s 16 and 17 controls the outputcurrent of the control transistor 14 by detecting the variation of theload voltage and a reference voltage, comparing such voltages, andamplifying the difference therebetween. The differential amplifier 16,17 supplies the amplified signal to the base electrode of the controltransistor 14. The power source voltage Vin is divided by a variableresistor 18 to provide the standard voltage Vc which is applied to thesecond F.E.T. 17 as the gate voltage. The standard voltage Vc and theload voltage Vo are maintained equal to each other by the balancingoperation of the first and second F.E.T.s l6 and 17.

It is assumed that the resistance of the photoconductive element 12varies with the variation in brightness of the object to bephotographed. If, for example, the equivalent resistance of the phtoconductive element 12 decreases, the load voltage V0 decreases and theoutput current of the first F.E.T. 16 decreases, since its gate voltageis decreased with respect to its source voltage Vs. Accordingly, thecurrent flowing through a source resistor 19 is decreased and the sourcevoltage Vs is decreased. Since Vo RoIo, V0 decreases when R0 decreasesand I0 is constant. R0 is the load resistance and I0 is the loadcurrent.

Since the F.E.T.s l6 and 17 have a common source, the output current ofthe second F.E.T. 17, that is, the drain current, increases when thesource voltage Vs decreases relative to the reference voltage Vc. VcsVc-Vs. When Vcs increases, drain current of 17 increases according tothe characteristic of the F.E.T. Therefore, the base current of thecontrol transistor 14 connected to the drain of the second F.E.T. l7,and accordingly the collector current, increases and the voltage acrossthe terminals 13 and 21 of the photoconductive element 12 increases. Inother words, the circuit operates to maintain a voltate Vc Vo byincreasing the load current when the load resistance decreases.

Although the foregoing description is for the case where the loadcurrent is decreased, the circuit of the invention operates to decreasethe load current when said load current is increased by the operation ofthe control transistor 14.

Thus, in the circuit of FIG. 2, an output current corresponding to theequivalent resistance of the photoconductive element 12 is obtained inorder to maintain the load voltage Vo constant at the output terminals13 and 21 of the constant voltage circuit. This means that an outputcurrent is obtained which is responsive to the brightness of the objectto be photographed. If a capacitor 22, having a capacitance C1, isconnected in the feedback circuit of the constant voltage circuit to cutoff the closed circuit, as shown in FIG. 2, and the connection at theoutput of the control transistor 14 is connected to said capacitance viathe switch 15 an output current responsive to the load resistance isprovided.

Since the capacitor 22 is connected to the gate of the first F.E.T. l6and the switch 15 is connected at the output of the constant voltagecircuit, the gate potential of said PET. is maintained even when saidswitch is switched in connection from the contact 15a to the contact15!). This is because the capacitor 22 is charged up to a voltagesubstantially equal to the constant load voltage V and it is maintainedundischarged due to the high input resistance of the first F.E.T. 16.

The switch 15 is switched from the contact 15a to the contact 15b at thetime of shutter release immediately before the mirror (not shown) ismoved up. Consequently, an output current of the control transistor 14proportional to the resistance of the photoconductive element 12,- whichhas the same magnitude as that of the closed circuit, is obtained at thecontact 15b of the switch 15. Then, when the mirror is moved up, thephotocell 12 is shielded from the light and the equivalent resistance ofthe said photocell becomes indefinitely large and all the output currentof the control transistor 14 flows through a trigger switch 23.

Accordingly, if the trigger switch 23 is opened simultaneously with therunning of the leading diaphragm (not shown), which is a shutter orcurtain, the time for charging a capacitor 24, having a capacitance C2,by the output current of the control transistor 14 is determined and theswitching circuit operates to make the trailing diaphragm (not shown)which is also a shutter or curtain run, which determines the shutterspeed by releasing the holding effect of the magnet for the trailingdiaphragm. The exposure time or shutter speed is determined by thebrightness of the object to be photographed. The resistance of thephotocell 12 is determined by the brightness of the object to bephotographed. The output current of the control transistor 14 in turn isproportional to the resistance of the photocell 12.

The desired shutter speed is provided by the capacitor 24 and a timingand switching circuit 25 connected thereto. The timing and switchingcircuit 25 controls the shutter (not shown) via a coil 26. The capacitor24 is connected to the circuit via the switch I and its contact b.

The circuit of the invention thus makes it possible to automaticallycontrol the exposure, even when photometric operation is impossible dueto the light shielding construction wherein the mirror is moved up. Thisis a known defect of an electric shutter in a single lens reflex cameraof the T.T.L. type.

In the embodiment of FIG. 3, the gain of the difference amplification isincreased in order to broaden the responsive range of the amount oflight. In the embodiment of FIG. 3, a memory element comprising acapacitor 27 is provided in the constant voltage circuit embodying thebasic principle of the invention. In FIG. 3, a switch 28 is provided foropening the closed circuit. The switch 15. takes out the output currentof the control transistor 14'. The capacitor 23 and the timing andswitching circuit 25' provide the desired shutter speed.

The circuit of FIG. 3 is similar to the circuit of FIG. 2, except thatthe gain of the feedback amplification and the difference amplificationis increased and the capacitor 27 for maintaining abalanced condition ischarged by the output current of a transistor 29. The transistor 29 isconnected to the second F.E.T. 117' and is part of the differentialamplifier I6, 17'. Furthermore, FIG. 3 includes a third F.E.T. 31 havinga high input impedance. The third F.E.T. 31 is used with the outputvoltage serving as the feedback signal and its output is connected andsupplied to the control transistor 14'.

In practical use, of course, a stable circuit is desired. In addition,as hereinbefore mentioned, it is also desired to increase the gain ofthe circuit to make the circuit responsive to a broad range of loadvariations in the amount of light from the object to be photographed.Especially when a field effect transistor is utilized, undesirablesignals such as hum are apt to be generated when the amount of lightfrom the object is small and the resistance of the photoconductiveelement is large. The balancing voltage of the capacitor 24 isinfluenced by these undesirable signals (FIG. 2) and results in shuttermisoperation. In the balance type circuit of the invention, theundersirable in-phase signals constituting noise, such as hum, is ableto be eliminated. Stable and reliable shutter control is provided byusing differential amplification and increasing the ratio of thedifferential gain to the in-phase gain (Common Mode Rejection ratio).

In the constant voltage circuit of the invention, it will be readilyunderstood that the exposure index can be changed by changing the valueto the reference voltage Vc provided by the variable resistor 18, andaccordihgly, the change in film speed (ASA) and in the size of thediaphragm may be c'zsily compensated.

In the embodiment of FIG. 4, a photocell or photoconductor 41 isdisposed in the path of light traversing the camera objective from theobject to be photographed and is connected via a double throw changeoverswitch 42 to the collector electrode of a current control transistor 43.The emitter electrode of the current control transistor 43 is connectedto the negative pole of a voltage source or battery 44 to provide anelectric current in series through the photoconductor 4i and thecollector-emitter path of the transistor 43. A timing capacitor 45 andthe photocell 41 are alternately connected to the collector electrode ofthe transistor 43 as the switch 42 is operatively changed over to itsopposite contacts 42a and 42b.

A deviated output or difference detecting circuit 46 is connected to theswitch 42 at a circuit point A at which the collector voltage of thetransistor 43 is provided. The difierence detecting circuit 46 comparesthe transistor 43 collector voltage at circuit point A with anothervoltage of a voltage divider 47 provided at a circuit point B of themovable. contact or electrode of said voltage divider. The voltagedivider 47 functions as a bleeder resistor and is connected across thevoltage source 44.

An amplifier 48 couples the output of the difference detecting circuit46 to the gate of an F.E.T. 49. A storage or memory capacitor 511 isconnected between the gate and source of the F.E.T. 49. An adjustablevoltage dividing point C at the movable contact or electrode of avoltage divider 52 which connects the source of the F.E.T. 49 to thevoltage source 44 is connected to the base electrode of the currentcontrol transistor 43. A switch 53 is connected between the amplifier 48and the gate of the F.E.T. 49 and is in operative engagement with asuitable camera mechanism such as a mechanism for opening the shutter(not shown) in a manner whereby said switch is opened just before thestart of the shutter release.

A switching circuit 54 controls an electromagnetic coil or winding 55upon application of the output from the amplifier 48. Theelectromagnetic coil 55 initiates the closing of the shutter. A powersource switch 56 is connected to The voltage source 44. A shunt switch57 is connected in parallel with the timing capacitor 45.

In operation of the embodiment of FIG. 4, it is assumed that thephotoconductor 41 is connected to the transistor 43 via the switch 42,and is exposed to light from the object to be photographed, and theswitches 56, 53 and 57 are closed before the shutter release. A dividedvoltage of the voltage or power source 44 develops at the circuit pointA dependent upon the resistance value of the photoconductor 41corresponding to the illumination intensity of the incident light. Theoutput of the difference detecting circuit 46 depends upon thedifference between the voltage at the potential dividing circuit point Bof the variable bleeder resistor 47 and the voltage at the circuit pointA is applied via the amplifier 48 to the gate of the F.E.T. 49.

As a result, the internal resistance of the transistor 43, determiningthe voltage at the circuit point A, is shifted in a manner whereby thevoltage between the circuit points A and B is reduced. Morespecifically, the drain current of the F.E.T. 49 depends upon thedetected output and the voltage at the circuit point C of the sourceresistor 52. Thus, an equilibrium condition is immediately establishedbetween the circuit points A and B, and an electric charge correspondingto the output of the difference detecting circuit 46 is stored in thestorage capacitor 51. When the storage operation is completed under thiscondition and the shutter release starts, the switch 53 is opened justbefore the start of the shutter release. The storage capacitor istherefore no longer charged. Once the release operation has started, thestorage capacitor 51 is free from any influence possible, even if thephotoconductor 41 is blocked from the light traversing the objective.

The subsequent operation before the shutter releases actuates the switch42 so that it contacts its contact 42b whereby the timing capacitor 45is connected to the collector electrode of the transistor 43, instead ofthe photocell 41. The shutter (not shown) is then opened and opens theshort-circuit switch 57. The transistor 43 accordingly controls thecurrent passing therethrough in the same manner as before the shutterrelease under the control of the F .E.T. 49, which receives as a controlsignal between its gate and source the terminal voltage of the storagecapacitor 51 depending upon the electric charge on said storagecapacitor. Thus, the current controlled by the transistor 43 is fed tothe timing capacitor 45 and is subject to a timing circuit operation bythe control current of said transistor and the capacitance of saidtiming capacitor. The controlled current then passes through thedifference detecting circuit 46 and the amplifier 48 and controls theoperation of the switching circuit 54, which controls the operation ofthe electromagnetic coil 55 to time the closing of the shutter.

The switching circuit 54 of the embodiment of FIG. 4 is actuated whetherthe switch 53 is open or closed. While the entire arrangement is in alight measuring condition, that is, during the period required for thecircuit points A and B to reach equilibrium, any action of the switchingcircuit 54 does not result in adverse effects on the movement of theshutter. The shutter is released after completion of the lightmeasurement and storage operations, and the switch 53 opens just priorto the shutter release. A common shutter closes in response to a closingsignal generated after the shutter opens. Accordingly, even if theswitching circuit 54 is actuated and the shutter closing signal isgenerated before the shutter is released, that is, before the shutteropens, it has no effect on the movement of the shutter.

There is no difference between an F.E.T. and a common transistor, sincethe resistance value between the drain and source may be varied by gatevoltage control. The term gate voltage control is used because the gateinput impedance is extremely high. When a specific voltage is appliedbetween the gate and source of the F.E.T. by a capacitor, the work ofthe F.E.T. may be maintained with small voltage consumption.

In the embodiment of FIG. 4, when the storage capacitor 51 is charged bythe output of the amplifier 48, the voltage between the drain and thesource of the F.E.T. 49 changes in response to the voltage between theterminals of said capacitor resulting from the charging of saidcapacitor. The output impedance of an F.E.T. is also high. If the outputsignal of the amplifier 48 to the storage capacitor 51 becomes higherthan previously, said capacitor is additionally charged and the F.E.T.49 is additionally changed. If the output signal of the amplifier 48becomes lower than previously, the storage capacitor 51 is dischargedthrough a transistor, hereinafter described with reference to FIG. 5,due to the amplifier utilized in the embodiment of FIG. 5, so that theelectric charge may become equal to the output value. Thus, when thebridge circuit has equal voltage at the circuit points A and B, theF.E.T. 49 maintains its operation by a gate voltage applied by thestorage capacitor 51. Even when the circuit point A has the same voltageas the circuit point B, the F.E.T. 49 is not cut off.

FIG. 5 illustrates an embodiment of the shutter control circuit of theinvention for use in a single lens reflex camera as do FIGS. 2 and 3. InFIG. 5, a photosensitive element 101, such as, for example, a photocellor photoconductor, is disposed in the path of light traversing theobjective from an object to be photographed. A bridge circuit comprisesthe photosensitive element 101, a transistor 102 and fixed resistors106. and 106". A difference detecting circuit 107, corresponding to thedifference detecting circuit 46 of FIG. 4, comprises a transistor, andis connected to output terminals A and B of the bridge circuit. Atransistor 108, corresponding to the amplifier 48 of FIG. 4, isconnected to the output of the transistor 107. A timing capacitor isselectively connected into the circuit via a changover switch 103alternately with the photosensitive element 101.

As in the embodiment of FIG. 4, a memory or storage circuit comprises anF.E.T. 109, a capacitor 110 and a source resistor 111. Feedback isprovided by connecting a voltage dividing circuit point C on theresistor 111 to the base electrode of the transistor 102. A shutterclosure release electromagnet 114 is controlled by a solid stateswitching circuit, including transistors 1 13' and 113". The input ofthe transistor 113" is connected to the output of the transistor 113;and the input of the transistor 113' is connected to the normally opencontact 112' of a make-and-break switch 112 which is series connectedvia its other terminal 112" to the circuit for charging the storagecapacitor 110. A shortcircuit switch 116 is connected in parallel withthe timing capacitor 105 in a manner whereby said switch is opened inresponse to the shutter opening operation.

A constant voltage diode 117 is connected in series between the sourceresistor 111 of the F.E.T. 109 and the negative polarity terminal of thepower or voltage source 104, which may comprise a battery. An adjustablediaphragm 118 is arranged in front of the photosensitive element 101.The diaphragm 116 is so arranged that the stopping value thereof isadjustably set according to a parameter other than the illuminationintensity of the object to be photographed, such as, for example, thesensitivity of film used and the present stopping value for a camera.

In the embodimnt of FIG. 5, the photosensitive element 101 is exposed tothe light from the object to be photographed during exposurepreparation, such as viewing the object, and the resistance valuethereof corresponding to the illumination intensity on saidphotosensitive element, as reflected by the output at the terminals Aand B of the bridge circuit, is detected by thetransistor 107, amplifiedby the transistor 108 and applied to the storage capacitor 110. Thus, asin the embodiment of FIG. 4, the bridge circuit is stabilized withrespect to the voltage across its output terminals A and B at a valuecorresponding to the illumination intensity of the object, since theF.E.T. 109 effectively controls the feedback current to the transistor102 included in the bridge circuit.

,During the first half of the depression path of the shutter releasebutton, (not shown) the make-andbreak switch 112 and the changeoverswitch 103 are changed over as shown by broken lines in FIG. 5. Duringthis operation, the electromagnet coil or winding 114 is energized andfunctions to prevent the shutter (not shown from being closed. Duringthe completion of the depression of the shutter release button, theshutter opening is initiated and the short-circuit switch 116 issimultaneously opened. At this point, the timing capacitor 105 begins tobe charged with the current controlled by the transistor 102. Thetransistor 102 is in turncontrolled by the feedback storage or memorycurrent under the control of the PET. 109. When the terminal voltage ofthe timing capacitor 105 reaches a predetermined value, the transistors107 and 108 operate as switching elements and are switched over to theconditions of the opposite phase at the instant of starting the release.The transistors 113' and 113" are also reversed, cutting off theenergization of the electromagnet winding 114. The shutter is thereforereleased from its locked open condition and is closed.

In the embodiment of FIG. 6, a photosensitive element 201 is located, asin the embodiments of FIGS. 4 and'5, in the path of light traversing theobjective from an object to be photographed. A current controltransistor 202 is series connected via a changeover switch 203 in thephotoelectric circuit of the photosensitive element 201. A battery 204functions as a power or voltage source. A timing capacitor 205 isconnected in parallel with the photosensitive element 201 via thechangeover switch 203. A first F.E.T. 221 has a gate to which theterminal voltage of the photosensitive element 201 and of the timingcapacitor 205 are alternately applied via the switch 203. A constantcurrent control transistor 202' is series connected to the source of thefirst F.E.T. 221.

A potential determining transistor 207 is connected between the movablecontact or electrode of a variable bleeder resistor 206 at a circuitpoint B" and a circuit point A" connected to the source of the firstF.E.T. 221 whereby a difference output of the transistor 207 is suppliedvia an amplifying transistor 208 to the base electrode of an outputtransistor 213 and to a storage or memory capacitor 210. The storagecapacitor 210 is connected between the gate and the source of a secondF.E.T. 209 via a source resistor 211' and a constant voltage diode 217(which may be a Zener diode) series connected to the source of saidsecond F.E.T., so that the source potential may be kept constant. Adischarge resistor 220 is connected in parallel with the storagecapacitor 210.

A negative feedback circuit derives a voltage responsive to the outputof the second F.E.T. 209 from the drain of said second F.E.T., at acircuit point C", and applies said voltage to the base electrode of thecurrent control transistor 202. The negative feedback circuit alsoconnects a common point in the connection between a resistor 211" andthe diode 217 to the base electrode of the constant current controltransistor 202'. A switch 212 is series connected between the amplifyingtransistor 208 and the storage capacitor 210 and is operativelyassociated with the camera mechanism (not shown) in a manner whereby itis opened just.

before shutter release.

The closing of the shutter (not shown) is controlled via outputterminals 219. A display lamp 222 may be series connected instead of acollector resistor 223 of the output transistor 213 or may be connectedin parallel with said collector resistor. A short-circuit switch 216 isconnected in shunt with the timing capacitor 205 and is-openedsynchronously with the opening of the shutter.

The embodiment of FIG. 6 operates as follows. As in the embodiments ofFIGS. 4 and 5, when the changeover switch 203 is closed by the firsthalf of the depression of the shutter button in a manner whereby thecollector electrode of the transistor 202 is connected to thephotosensitive element 201, a divided voltage of the battery 204 isapplied to the gate of the first F.E.T. 221. The output of the potentialdetermining transistor 207 is controlled by the difference voltagebetween the voltage at the source of the first F.E.T. 221 at the circuitpoint A" corresponding to the divided voltage applied to the gate ofsaid F.E.T., and the voltage at the circuit point B on the variablebleeder resistor 206. At this point, the transistor 202 functions as aconstant current control element. The determined output is appliedthrough the amplifying transistor 208 to the second F.E.T. 209 and,under the control of said second F.E.T., is fed back to the baseelectrode of the transistor 202. The transistor 202 therefore shifts inaccordance with the determined output in such a manner that saidtransistor controls the current passing therethrough so that it shiftsthe voltage between the circuit points A" and B". An equilibriumcondition is thus instantly established between the circuit points A."and B".

The storage capacitor 210 is charged an amount corresponding to thedetermined output of the transistor 207 at the instant of equilibrium.When the storage or memory operation is completed and the shutterrelease is initiated, the shutter release operation sequence is effectedin the same manner as in the embodiments of FIGS. 4 and 5. During theshutter release control, the timing capacitor 205 considerably loses itscharacteristic of linear variation with respect to both the elapsedtime, based on the charging current, and the value of the terminalvoltage due to leakage current, which is shown in broken lines as anequivalent leakage resistor 224 connected in shunt with the timingcapacitor, while the terminal voltage of the storage capacitor 210gradually decreases due to the action of the discharge resistor 220. I

The decrease in voltage of the storage capacitor 210 results in theshifting of the negative gate voltage on the second F.E.T. 209 in apositive direction, since the circuit point C" at the source of saidsecond F.E.T. is maintained constant by the constant voltage diode 217.Accordingly, the drain current of the second F.E.T. 209 graduallyincreases as time lapses, and the feedback current to the constantcurrent control transistor 202' shifts further in the negativedirection. Thus, the current through the current control transistor 202,that is, the charge current to the timing capacitor 205, graduallyincreases.

The storage capacitor 210 serves to maintain the gate voltage of thesecond F.E.T. 209, so that the capacitance thereof may be selectedwithin a relatively wide range. Therefore, the capacitance of thestorage capacitor 210 and the resistance value of the discharge resistor220 may be properly selected in order that the variation in the draincurrent of the second F.E.T. 209 with time is adjusted in a mannerwhereby it compensates for the leakage current of the timing capacitor205.

Although the leakage current can be compensated in the aforedescribedmanner, shutter control via the aforedescribed circuit is impossibleunder light conditions in which the resistance value of thephotosensitive element 201 exceeds the maximum resistance value of thecurrent control elements such as the transistor 202. Such lightconditions are beyond the limit within which photographing is possible.If the display lamp 222 is connected to the collector electrode of theoutput transistor 213 in the embodiment of FIG. 6, a voltage at thecircuit point A" is substantially equal to a voltage at the potentialdividing circuit point B" while 'the gate voltage of the second F.E.T.209 is of slightly greater positive voltage range than the gate cutoffvoltage, as far as the bridge circuit is maintained in equilibrium. Thevoltage at the circuit point C" at the source terminal of the storagecapacitor 210 for holding the gate voltage of the second F.E.T. 209 isproperly selected whereby the output transistor 213 becomes conductivewith the output of the amplifying transistor 208 under theaforedescribed equilibrium condition. The display lamp 222 is thusenergized. The display operation indicates that the object to bephotographed is of an illumination intensity within the range whereexposure can be automatically adjusted and that the storage or memoryoperation has been completed.

On the other hand, under extremely low illumination conditions,resulting in a corresponding resistance value of the photosensitiveelement 201, if the transistor 202 cannot correspond to the resistancevalue despite the regulating operation by the feedback, due to darkcurrent of said transistor, the voltage at the circuit point A"maintains the positive voltage for a longer time than the voltage at thecircuit point B" does. The gate voltage of the second F.E.T. 209 is thusmore negative than that under equilibrium conditions and also thebasevoltage of the output transistor 213 is within the negative range. Thedisplay lamp 222 is therefore deenergized.

In the embodiment of FIG. 6, therefore, the display lamp 222 indicatesthat a given object to be photographed is of an illumination intensitywithin the range where exposure can be automatically adjusted. It shouldbe noted that an electromagnetic coil or winding may be utilized insteadof the display lamp 222 as used in the embodiment of FIG. 6. Theelectromagnetic coil would operate to provide an indication display or acolor display in a viewfinder.

While the invention has been described by means of specific examples andin specific embodiments, it is not limited thereto, for variousmodifications may be made without departing from the spirit and scope ofthe invention. Those elements or features referred to above asunillustrated are to be understood as per se known.

What is claimed is:

l. A shutter control circuit for the shutter of an automatic camerasuccessively movable to open and closed positions defining an exposuresequence, said shutter control comprising shutter control means foropening and closing the shutter;

photosensitive means exposed to light when the shutter is in a lightmeasuring phase and unexposed to light when the shutter is open;

circuit means connected to the photosensitive means for providing afirst signal corresponding to a variation of the voltage across thephotosensitive means due to a variation in the intensity of lightimpinging thereon;

reference voltage means for providing a reference voltage;

comparing means connected to the circuit means and to the referencevoltage means for comparing the first signal and the reference voltageand for providing a difierent signal representing the difference betweensaid first signal and said reference voltage; and

control means coupling the comparing means a. to the shutter controlmeans in accordance with the shutter position for controlling theshutter speed in accordance with the variation of the voltage across thephotosensitive means;

b. to the photosensitive means in accordance with the shutter positionto control the voltage across said photosensitive means and therebyprovide equilibrium between the voltage across the photosensitive meansand the reference voltage; and

. information storage means coupled to the comparing means in accordancewith the shutter position for storing a signal corresponding to thedifference signal when the shutter is in a preexposure position and thephotosensitive means is exposed to light and coupled to the shuttercontrol means in accordance with the shutter position.

2. A shuttercontrol circuit as claimed in claim 1, wherein thephotosensitive means comprises a load and the circuit means comprises afeedback circuit connected to the photosensitive means for providing afeedback signal corresponding to a variation of the load voltage.

3. A shutter control circuit as claimed in claim 2, wherein thecomparing means comprises a differential amplifier and amplifies thedifference signal.

4. A shutter control circuit as claimed in claim 3, wherein the controlmeans includes a control transistor.

5. A shutter control circuit as claimed in claim 4, wherein thephotosensitive means comprises a photosensitive cell and the feedbackmeans comprises a first field effect transistor and switching means forselectively connecting the first field effect transistor to the controltransistor and to the photosensitive cell.

6. A shutter control circuit as claimed in claim 4, wherein thecomparing means comprises adifferential amplifier having a first fieldeffect transistor and a second field effect transistor connected to saidfirst field effect transistor.

7. A shutter control circuit as claimed in claim 6, wherein the firstfield effect transistor has a gate electrode connected via the switchingmeans to the control transistor and to the photosensitive cell, a drainelectrode coupled to the control transistor and a source electrode, andthe second field effect transistor has a source electrode directlyconnected to the source electrode of the first field effect transistor,a drain electrode coupled to the control transistor and a gate electrodeconnected to the reference voltage means.

8. A shutter control circuit as claimed in claim 7, wherein the shuttercontrol means includes timing means, and the information storage meanscomprises a capacitor connected to the timing means and connected to thecontrol means via the switching means in accordance with the shutterposition.

9. A shutter control circuit as claimed in claim 8, further comprisingconstant voltage means connected in the feedback circuit.

10. A shutter control circuit as claimed in claim 9, wherein theconstant voltage means comprises another capacitor connected to the gateelectrode of the first field effect transistor.

11. A shutter control circuit as claimed in claim 9, further comprisinga second transistor connected to the drain electrode of the second fieldeffect transistor and a third field effect transistor coupled to thesecond transistor and connected to the control transistor.

12. A shutter control circuit as claimed in claim 11, wherein theconstant voltage means comprises another capacitor connected to the gateelectrode of the third field effect transistor.

13. A shutter control circuit as claimed in claim 12, further comprisinga switch connected between the seond transistor and the third fieldeffect transistor for selectively opening the circuit.

14. A shutter control circuit, comprising a storage network comprising abridge circuit including outputs, a resistance section having aresistance which is adjustable according to information to be stored anda current control section adapted to be controlled according to feedbackstorage quantity;

a capacitor;

switch means;

a charging circuit for said capacitor connected through said switchmeans to an outputof said bridge circuit;

a field effect transistor having an input connected to said capacitorand an output connected to said bridge circuit, said field effecttransistor feeding back a controlled electricity quantity to thecurrentcontrol section of said bridge circuit; and

electrical determining means connected via said switch means to theresistance section of said bridge circuit.

15. A shutter control circuit as claimed in claim 14, further comprisinga discharge resistor connected across said capacitor.

16. A shutter control circuit as claimed in claim 14, further comprisingdisplay means coupled to the bridge circuit for providing a displaysignal in response to the output of said bridge circuit.

17. A shutter control circuit having an electrical feedback photometriccircuit for a camera comprising a photosensitive means exposed to lightpassing through an objective lens when the camera shutter is in aphotometric phase and unexposed to light when the shutter is opened;

a reference voltage means pre-adjusted in accor dance with photographingparameters including a diaphragm or film sensitivity;

a comparing means for comparing a first signal determined correspondingto output of said photosensitive means with a second signal defined atsaid reference voltage means and for producing a third signalcorresponding to said first and second signals;

a feedback coupling circuit for controlling its output corresponding tothe produced third signal of said comparing'means and for coupling itsoutput to said photosensitive means in a photometric phase thereof;

an information storage means connected to said comparing means formaintaining output of said feedback coupling circuit corresponding tolight incident on the photosensitive means prior to the opening of theshutter;

a shutter actuating circuit for determining exposure time applied tooutput of a control transistor determined in accordance with theinformation storage means when the shutter is opened; and

a coupling means for coupling a stabilized signal maintained by saidinformation storage means to said shutter actuating circuit so as not tobe influenced by the photosensitive means prior to its output beingvaried.

18. A shutter control circuit as claimed in claim 17, wherein saidinformation member comprises a photoconductor.

19. A shutter control circuit as vclaimed in claim 18, furthercomprising a timing capacitor and switching means for alternatelyconnecting said photo-conductor and said timing capacitor to said firsttransistor.

20. A shutter control circuit as claimed in claim 18, wherein said firstand second means define a bridge circuit having a pair of legs includingresistors and other legs each including a corresponding one of saidphotoconductors and said first transistor.

21. A shutter control circuit as claimed in claim 20, wherein at leastone of the resistors of the bridge legs is variable.

22. A shutter control circuit as claimed in claim 17, further comprisinga solid state switch, a shutter closure release member controlled bysaid solid state switch, and switching means for selectively openingsaid negative feedback network at said amplifier input and coupling saidthird means to the input of said solid state switch.

23. A shutter control circuit as claimed in claim 17, wherein saidfeedback network includes a bridge circuit includingsaid firsttransistor and having opposite sistor.

1. A shutter control circuit for the shutter of an automatic camerasuccessively movable to open and closed positions defining an exposuresequence, said shutter control comprising shutter control means foropening and closing the shutter; photosensitive means exposed to lightwhen the shutter is in a light measuring phase and unexposed to lightwhen the shutter is open; circuit means connected to the photosensitivemeans for providing a first signal corresponding to a variation of thevoltage across the photosensitive means due to a variation in theintensity of light impinging thereon; reference voltage means forproviding a reference voltage; comparing means connected to the circuitmeans and to the reference voltage means for comparing the first signaland the reference voltage and for providing a different signalrepresenting the difference between said first signal and said referencevoltage; and control means coupling the comparing means a. to theshutter control means in accordance with the shutter position forcontrolling the shutter speed in accordance with the variation of thevoltage across the photosensitive means; b. to the photosensitive meansin accordance with the shutter position to control the voltage acrosssaid photosensitive means and thereby provide equilibrium between thevoltage across the photosensitive means and the reference voltage; andc. information storage means coupled to the comparing means inaccordance with the shutter position for storing a signal correspondingto the difference signal when the shutter is in a pre-exposure positionand the photosensitive means is exposed to light and coupled to theshutter control means in accordance with the shutter position.
 2. Ashutter control circuit as claimed in claim 1, wherein thephotosensitive means comprises a load and the circuit means comprises afeedback circuit connected to the photosensitive means for providing afeedback signal corresponding to a variation of the load voltage.
 3. Ashutter control circuit as claimed in claim 2, wherein the comparingmeans comprises a differential amplifier and amplifies the differencesignal.
 4. A shutter control circuit as claimed in claim 3, wherein thecontrol means includes a control transistor.
 5. A shutter controlcircuit as claimed in claim 4, wherein the photosensitive meanscomprises a photosensitive cell and the feedback means comprises a firstfield effect transistor and switching means for selectively connectingthe first field effect transistor to the control transistor and to thephotosensitive cell.
 6. A shutter control circuit as claimed in claim 4,wherein the comparing means comprises a differential amplifier having afirst field effect transistor and a second field effect transistorconnected to said first field effect transistor.
 7. A shutter controlcircuit as claimed in claim 6, wherein the first field effect transistorhas a gate electrode connected via the switching means to the controltransistor and to the photosensitive cell, a drain electrode coupled tothe control transistor and a source electrode, and the second fieldeffect transistor has a source electrode directly connected to thesource electrode of the first field effect transistor, a drain electrodecoupled to the control transistor and a gate electrode connected to thereference voltage means.
 8. A shutter control circuit as claimed inclaim 7, wherein the shutter control means includes timing means, andthe information storage means comprises a capacitor connected to thetiming means and connected to the control means via the switching meansin accordance with the shutter position.
 9. A shutter control circuit asclaimed in claim 8, further comprising constant voltage means connectedin the feedback circuit.
 10. A shutter control circuit as claimed inclaim 9, wherein the constant voltage means comprises another capacitorconnected to the gate electrode of the first field effect transistor.11. A shutter control circuit as claimed in claim 9, further comprisinga second transistor connected to the drain electrode of the second fieldeffect transistor and a third field effect transistor coupled to thesecond transistor and connected to the control transistor.
 12. A shuttercontrol circuit as claimed in claim 11, wherein the constant voltagemeans comprises another capacitor connected to the gate electrode of thethird field effect transistor.
 13. A shutter control circuit as claimedin claim 12, further comprising a switch connected between the secondtransistor and the third field effect transistor for selectively openingthe circuit.
 14. A shutter control circuit, comprising a storage networkcomprising a bridge circuit including outputs, a resistance sectionhaving a resistance which is adjustable according to information to bestored and a current control section adapted to be controlled accordingto feedback storage quantity; a capacitor; switch means; a chargingcircuit for said capacitor connected through said switch means to anoutput of said bridge circuit; a field effect transistor having an inputconnected to said capacitor and an output connected to said bridgecircuit, said field effect transistor feeding back a controlledelectricity quantity to the current control section of said bridgecircuit; and electrical determining means connected via said switchmeans to the resistance section of said bridge circuit.
 15. A shuttercontrol circuit as claimed in claim 14, further comprising a dischargeresistor connected across said capacitor.
 16. A shutter control circuitas claimed in claim 14, further comprising display means coupled to thebridge circuit for providing a display signal in response to the outputof said bridge circuit.
 17. A shutter control circuit having anelectrical feedback photometric circuit for a camera comprising aphotosensitive means exposed to light passing through an objective lenswhen the camera shutter is in a photometric phase and unexposed to lightwhen the shutter is opened; a reference voltage means pre-adjusted inaccordance with photographing parameters including a diaphragm or filmsensitivity; a comparing means for comparing a first signal determinedcorresponding to output of said photosensitive meaNs with a secondsignal defined at said reference voltage means and for producing a thirdsignal corresponding to said first and second signals; a feedbackcoupling circuit for controlling its output corresponding to theproduced third signal of said comparing means and for coupling itsoutput to said photosensitive means in a photometric phase thereof; aninformation storage means connected to said comparing means formaintaining output of said feedback coupling circuit corresponding tolight incident on the photosensitive means prior to the opening of theshutter; a shutter actuating circuit for determining exposure timeapplied to output of a control transistor determined in accordance withthe information storage means when the shutter is opened; and a couplingmeans for coupling a stabilized signal maintained by said informationstorage means to said shutter actuating circuit so as not to beinfluenced by the photosensitive means prior to its output being varied.18. A shutter control circuit as claimed in claim 17, wherein saidinformation member comprises a photoconductor.
 19. A shutter controlcircuit as claimed in claim 18, further comprising a timing capacitorand switching means for alternately connecting said photo-conductor andsaid timing capacitor to said first transistor.
 20. A shutter controlcircuit as claimed in claim 18, wherein said first and second meansdefine a bridge circuit having a pair of legs including resistors andother legs each including a corresponding one of said photoconductorsand said first transistor.
 21. A shutter control circuit as claimed inclaim 20, wherein at least one of the resistors of the bridge legs isvariable.
 22. A shutter control circuit as claimed in claim 17, furthercomprising a solid state switch, a shutter closure release membercontrolled by said solid state switch, and switching means forselectively opening said negative feedback network at said amplifierinput and coupling said third means to the input of said solid stateswitch.
 23. A shutter control circuit as claimed in claim 17, whereinsaid feedback network includes a bridge circuit including said firsttransistor and having opposite output terminals connected to the baseand emitter electrodes of said first transistor.
 24. A shutter controlcircuit as claimed in claim 17, further comprising a field effecttransistor having a source electrode and a potentiometer having aresistance element connected in series with the source electrode of saidfield effect transistor and a movable contact connected to the baseelectrode of said first transistor.